Hi Ron,
The situation becomes increasingly more critical as the compression
ratio goes up. It is worthy of attention at 7 to 1 & I would consider
the stock Healey Sixes at 9 to 1 to be quite critical. As I said,
better to limit the MAXIMUM advance to 32 to 36 degrees, than to be sorry.
My BN2 at 7.5 to 1 was not too critical of maximum advance. With it
now raised to 9.5 to 1, it is very critical.
If the head or block is decked (milled) in the rebuild process, as is
often done to true the surfaces, the compression ratio will be even
higher than the original.
Regards,
Dave Russell
BN2
Ron Fine wrote:
> Hi Dave, for those of us still learning, could you define "high
> compression engines"? Is a stock rebuilt 3000 Healey engine a high
> compression engine? Thanks, Ron ----- Original Message ----- From:
> "Dave & M" <rusd@velocitus.net> To: "Michael Salter"
> <msalter@precisionsportscar.com> Cc: "HealeyList"
> <healeys@autox.team.net> Sent: Tuesday, January 09, 2007 12:23 PM
> Subject: Re: Pistons damaged again
>
>
>> Hi Folks,
>>
>> I tell this to everyone who will listen, but few apparently do.
>>
>> On high compression engines, it is important to set ignition
>> timing at an rpm where maximum static plus centrifugal advance
>> (vacuum advance not connected) is all of the way in. Depending
>> on the particular distributor, this could be anywhere from 4,000
>> to 5,000 rpm. Most engines will tolerate between 32 & 36 degrees
>> of total maximum advance, depending on engine tune, fuel grade, &
>> altitude. In other words, set for maximum advance & let the idle
>> advance fall where it may.
>>
>> It seems that many folks still insist on setting advance at idle
>> & letting the maximum advance fall where it may. This method is
>> not precise. The distributor's initial centrifugal advance curve
>> is very steep (advances quickly) at low rpm. Only a small error
>> in the rpm that the advance is set at can make a very large error
>> in the total advance at high rpm.
>>
>> Seat of the pants timing is never reliable. A few degrees of over
>> advance "may" give better throttle response & a bit more overall
>> power, But the risks are great.
>>
>> ------------------ Quote Michael Salter: Detonation can be quite
>> serious at highway speeds but completely inaudible to the driver.
>> You can buy knock sensors which will turn on a light when
>> detonation is occurring; might be a good investment.
>> ------------------ Quote Bob Spidell: "I'm not convinced that the
>> fuels that are available today, particularly in CA I understand,
>> are good enough to handle the amount of advance that the original
>> distributors can produce. " -----------------
>>
>> I agree completely with Michael & Bob.
>>
>> Regards, Dave Russell BN2
|